A method to operate and control one example of an electrically controlled actuator is described in U.S. Pat. No. 5,494,219. This patent presents a method for controlling opening and closing coils of a dual coil fuel injector. The opening and closing coils are used to create electromagnets that may be made to open and close the fuel injector during engine operation. An injector opening cycle is described by a sequence where current is supplied to the closing coil before current is applied to the opening coil. Current is applied to the closing coil with the objective of overcoming residual magnetism that remains in the closing electromagnet core. By attempting to overcome the residual magnetism, the method seeks to negate the latching effect that the residual magnetism provides between the electromagnet and the armature.
The above method also has several disadvantages. For example, the current profile that is delivered to the opening coil for the purpose of overcoming the residual magnetism of the electromagnet is constant from operating cycle to operating cycle and equivalent between different fuel injectors. However, the amount of residual magnetism present within a group of magnet cores can vary with operating conditions, manufacturing variations, and past operating history. Consequently, the method's constant current profile, which is intended to counter the residual magnetic force left in the closing electromagnet, will likely cause the closing electromagnet to produce a counter magnetic force that does not properly cancel the residual magnetism. In other words, the closing electromagnet can retain its residual magnetism and latching capacity, which will have to be overcome by the magnetic field generated by the opening electromagnet if the actuator is to change its operating state. To counteract this imbalance, the opening electromagnet magnetic field may be strengthened by increasing current flow to the electromagnet; however, additional current supplied to the opening coil may cause coil degradation during some conditions and would require a valve controller having a higher current capacity. In addition, when operating at colder operating temperatures, friction between the actuator armature and the armature guiding surfaces can increase such that still additional current may be needed to change the actuator state. And since the method does not have the capacity to precisely counteract the residual magnetism, current may have to be increased in the opening electromagnet to overcome the remaining residual magnetism as well as the increased friction. These conditions may increase the possibility of opening coil degradation if the opening coil is used to overcome both the residual magnetism and the friction forces.